Applying a self-levelling compound to a concrete floor

Summary: Learn how to apply a self-levelling compound to a concrete floor.

If you want to fit any form of floor covering to a concrete floor with a rough surface, the only practical subfloor is a self-levelling compound. This is a latex-based compound that provides a very smooth finish but, despite its name, it will need some degree of levelling with a plastering trowel. Laying this form of subfloor will raise the floor slightly, so the bottom of any doors opening into the room may need to be trimmed.

Preparation

Thoroughly clean the floor, removing any loose debris and as much dust as possible.

Remove any previous bitumen-based layer or old tile adhesive.

A dusty floor surface needs to be primed with a PVA solution: mix 4 parts water and 1 part PVA.

Using a wide paintbrush apply the PVA solution over the floor's surface.

To prevent the smoothing compound seeping into the adjoining room or rooms, fix a threshold strip across any doorways.

Applying the compound

When the floor is dry, mix the compound according to the manufacturer's instructions in a clean bucket to avoid contamination. A power stirrer is ideal for stirring as it prevents too much air getting into the mix.

Pour some of the compound onto the floor at your chosen starting point, usually one of the farthest corners of the room.

Use a plastering trowel to smooth the compound evenly over the floor. The compound should be about 5mm (1/5in) thick, although this will depend on how uneven the existing floor is. Ensure all indentations are filled and any high spots are levelled.

Continue to mix and spread the compound until the whole floor is covered, tying each new section into the damp edges of the sections you have already laid. Self-levelling compound only remains workable for about 30 minutes so you will need to work quickly.

Allow the compound to dry overnight. The following day use a medium grade sandpaper block to smooth away any ridges caused by the trowelling.